The present invention relates to an oil pump, for example, for supplying lubrication oil to sliding sections of an automotive vehicle or for supplying pressurized oil to a power cylinder of a power steering system for assisting steering.
An oil pump, for example, for use in automotive vehicles has a pump housing and a housing cover that are made of an aluminum alloy of a small specific gravity. The oil pump further has a cam ring made of an iron-system material, which cam ring is required to have a large strength.
In case, as described above, the pump housing and the housing cover are made of a metal of a larger line expansion coefficient and the cam ring is made of a metal of a smaller line expansion coefficient, they make different displacements due to thermal expansion in accordance with a temperature rise of working oil in the pump, thus increasing side clearances between them.
As a result, there occurs leakage of working oil through the side clearances and therefore a decrease in the pump efficiency.
Thus, there has been proposed, as disclosed in Japanese Utility Model Publication No. 58-183992, such an oil pump in which a spacer is disposed in a space surrounded by a housing and a housing cover, which spacer has a thermal expansion coefficient that compensates for an increase of a side clearance due to a difference in thermal expansion between a pump operating section and its surrounding section and which spacer has a sealing function to prevent leakage of working oil through the side clearance.